As is well known, a wide variety of different products in the form of powders or small particles are converted into larger end use forms such as prills, flakes, granules, pills, caplets, tablets, wafers, briquettes, pucks, and the like. In producing such products, it is common to utilize materials known as binders. Such materials, when mixed in suitable proportions with the powder or small particles to be compacted, facilitate the production of materials having desirable physical and mechanical properties. While some binders have relatively broad application to various powdery or small particle sized products, there are a number of instances where the binder can only be used for compaction of certain products and not for others. A principal reason for such limitation is chemical incompatibility as between the binder and certain powdery or small particle sized materials. A second reason for such limitation relates to the property of certain binders to modify the solubility characteristics of the powdery or finely-divided substrate material. For example, some binders are chosen not only for their ability to facilitate compaction, but to enable more rapid disintegration of the compacted form of the material, e.g., for more rapid dissolution in water.
If the solid active ingredient dissolves too quickly for optimum performance, the active ingredient is wasted. Conversely, with a binder that retards dissolution, a much more consistent dose of the active ingredient could be applied. This would be advantageous in the area of water treatment, where, if the dissolution of a solid active ingredient such as a biocide or cleaning agent could be retarded, there would be a longer time between reapplications of the biocide or cleaning agent. Waxes have been studied in the slowing and control of the delivery of ammonium phosphate fertilizers, as reported by S. M. Al-Zahrani in Ind. Eng. Chem. Res, 39, 367–371, 2000. Al-Zahrani observed that fertilizer formulations which were made by melt-blending the fertilizers with 10 wt % paraffin wax or 10 wt % polyethylene wax resulted in a twofold retardation of the dissolution rate as compared to the same fertilizer in the absence of wax.
One type of material that tends to be difficult to produce in compacted forms such as tablets, granules, and briquettes is halogenated hydantoins, especially N,N′-dihalogenated dialkylhydantoin products such as 1,3-dichloro-5,5-dimethylhydantoin, N,N′-bromochloro-5,5-dimethylhydantoin, and 1,3-dibromo-5,5-dimethylhydantoin. Such materials are useful as biocides for treating water such as recreational water, cooling water, process water, and wastewater.
The N,N′-dihalogenated dialkylhydantoin products are usually formed as powdery solids. For use in many applications such as water treatment, the dry powders need to be converted into larger forms such as granules, tablets, or briquettes. This in turn has presented problems associated with providing densified or compacted products with sufficient strength to withstand the physical stresses encountered in packaging, conveying, handling, shipping, storage, and use. The nature of these problems have been described, for example, in U.S. Pat. Nos. 4,532,330; 4,560,766; 4,654,424; 4,677,130; 4,745,189; and 5,565,576. The approaches described in these patents for alleviating one or more such problems involve use of other materials. Thus in U.S. Pat. Nos. 4,532,330 and 4,621,096, halogenated dimethylhydantoins are mixed with calcium chloride and water, and the mixture is compacted by compression into the desired shape. In U.S. Pat. Nos. 4,560,766 and 4,654,424, halogenated ethylhydantoins are used instead of halogenated dimethylhydantoins and are compacted as such, or are melt blended with halogenated dimethylhydantoins. U.S. Pat. No. 4,677,130 describes forming dry blends of the halogenated dimethylhydantoin with particulate alkali metal or alkaline earth metal salt followed by compression to form a compacted product such as a tablet.
Manufacturers of halogenated hydantoins have sought to overcome these limitations by blending the materials with process additives designed to improve compaction characteristics. The presence of other halogenated hydantoins has also been indicated to provide benefits. For example, published PCT Application WO 97/43264 describes the use of 1,3-bromochloro-5-methyl-5-propylhydantoin as a binder in making compacted forms of halogenated hydantoins. The presence of hydantoins having at least one ethyl group in the 5-position is indicated to provide free flowing, dust-free powders which can be compressed into shapes without resorting to binders, as detailed in U.S. Pat. Nos. 4,427,692 and 4,560,766. In U.S. Pat. No. 4,677,130 a series of inorganic salt additives ranging from sodium carbonate to sodium metasilicate was indicated to improve the crush strength of halogenated hydantoin tablets. Inert binders such as fatty acid salts and a hectorite clay were advocated in U.S. Pat. No. 5,756,440, while the use of fatty acid amide binder additives were described in U.S. Pat. No. 5,565,576 and indicated to improve the compaction properties of halogenated hydantoins. U.S. Pat. No. 5,780,641 describes a chemical composition comprising a halogenated hydantoin mixed with dry calcium hydroxide for the purpose of facilitating processing and achieving a shape-retentive form.
Unfortunately, almost all prior efforts in the compaction of halogenated hydantoins have not provided binders having satisfactory compaction characteristics along with good chemical compatibility. Some of the classical binders (e.g., polyvinylpyrrolidinone, cellulose compounds, glues, gums, sugars, and starches) which are used to compact other products would react with halogenated hydantoins, in some cases vigorously. Moreover, a number of binder systems proposed for use with halogenated hydantoins do not provide compacted products having sufficient physical and mechanical stability. Low crush strength is often another deficiency of such compacted products.
In commonly-owned copending application Ser. No. 09/487,816 a new type of binding agent for powdery or finely-divided materials, including halogenated hydantoins, has been discovered. These binders, micronized synthetic polyolefin-based hydrocarbon waxes, produce compacted compositions of great mechanical and physical strength. Furthermore, these binders are strongly hydrophobic, and consequently can be used for modifying the dissolution or release rate of the compacted material in aqueous media.
While this is very effective, it would be desirable to minimize the amount of binder used. This would allow the delivery of more halogenated hydantoin per unit compacted composition to the end user.
This invention provides a way to minimize the amount of binder used. At the same time, the granulation productivity is further improved, and surprisingly, slower dissolution rates (and longer product life) are observed with lesser amounts of binder.